In the ink supply into the recording head in an ink jet recorder, it is necessary that the pressure of ink acting on the recording head be maintained constant and that air bubbles be not included in the ink. As a matter of fact, however, in a conventional ink supplier of this type in which as described, e.g., in JP H06-106731 A, a subsidiary ink reservoir is used in addition to a main ink reservoir for ink storage and operated to supply ink during the recording and the main ink reservoir is operated to replenish ink when the amount of ink in the subsidiary ink reservoir becomes less than an established value, an ink supply pump is used to supply ink into the recording head from the subsidiary ink reservoir and the subsidiary ink reservoir is provided with an air vent such that the liquid level of ink in the subsidiary ink reservoir may communicate through it with the atmosphere.
In the conventional ink supplier described above, a fluctuation in operation of the ink supply pump used to supply ink into the recording head may cause the ink supply pressure on the recording head to fluctuate and in turn cause printing to become unstable. Further, the reservoir (subsidiary ink reservoir) for ink supply to the recording head is provided with the air vent where air in the environment communicates with the ink surface in the reservoir, via which air is entrained into ink in the reservoir. Such entrained air may, when fed to the recording head while being carried in ink, hinder the ink from being discharged out of the recording head in the form of properly regulated, successive droplets.
Further, in the ink jet recorder it is desirable that the pressure of ink supply to the recording head be made optimum individually for each of its operating states, namely during purging, initial charging, printing, wiping of the recording head and cleaning of a wiping blade.
For this purpose, conventional ink suppliers have been designed, as described in JP H11-20180 A and H07-137286 A, to change the ink pressure acting on the recording head by physically raising or lowering the ink reservoir as the ink source to the recording head to change the position head of the ink liquid level in the ink reservoir depending on those states such as printing, wiping of the recording head and others.
To wit, all these conventional ink suppliers have been designed to adjust the height of the ink liquid level relative to the recording head by vertically moving the ink reservoir (main ink reservoir) disposed directly ahead of the recording head for ink supply thereto. It has also been done to control the height (position head) of the ink liquid level by way of software upon measuring the ink supply pressure.
In ink jet recorders for industrial purposes, however, in which their continuous operation is essential, the ink reservoirs must be large in capacity, requiring that they be proportionally large in size and volume, too. Consequently, the drive source and structure need to raise and lower such a main ink reservoir cannot but be large-scaled with conventional techniques, presenting problems in terms of space of placement and manufacturing cost.
Also, as the ink reservoir becomes larger in size, the liquid level becomes controllable less reactively to the ink reservoir raised or lowered. Further, controlling the position head of the ink liquid level by way of software upon measuring the ink supply pressure makes the controller complicated and thus poses the cost problem.